-- FLEXIcontent 2.0.x for J2.5 is compatible with FC v1.5.x for J1.5 , DB schema , data formats, and configuration. So if you upgrade Joomla to J2.5 and install FC v2.0, it will work, but some places need updating:
(a) XML format of custom template (if you don't have custom template, then nothing to do) read how to here
(b) a few places need to be reconfigured, minigallery fields and FC load-module fields
In order to upgrade:
-- do a copy of your site, and upgrade to latest version available for J1.5
-- upgrade Joomla to 2.5, via Jupgrade (NOTE THIS WILL FLATTEN your category tree * we will provide a modified version that does not flatten the category tree)
-- install FLEXIcontent for J2.5+
-- and then manually update FC templates (see FAQ article) and re-save configuration to plugins that need it
-- move 'jupgrade' folder to ../public_html_new , rename you 'public_html' as 'public_html_old' and then rename 'public_html_new' as 'public_html'
FLEXImigrate is a free 3rd-party tool to handle the FLEXIcontent data migration process.
More info – Download FLEXImigrate
(you must register and log-in to download)
Always have a current full back-up before doing any migration on a live website.
It is highly recommended that you test the entire migration process on your local development site first.